1. Field of the Invention
The present invention relates to a method and device for detecting azimuth (i.e., azimuth direction, orientation, or direction) of a target based on a reflected wave from the target received by a plurality of receiving antennas.
2. Description of the Related Art
Conventionally, a radar device, called a phase-monopulse radar device, is known in which a plurality of receiving antennas receive a reflected wave emitted from a transmitting antenna and returned by being reflected by a target, and an azimuth of the target is detected from a shift in phase (in other words, phase difference) of a receiving signal at each receiving antenna.
However, when the azimuth is detected using phase difference, so-called aliasing (ambiguity) occurs based on the inability to differentiate between phase differences Δφ and Δφ+360°. Therefore, a problem occurs in that the azimuth can only be uniquely identified within a range in which the phase difference changes 360° (such as −180°<Δφ≦180°).
Therefore, a method is proposed in which, through use of a plurality of transmitting antennas each having a different beam directivity, and successive switching between the transmitting antennas, an azimuth detection range is widened using information (direction and beam width) regarding a transmission beam that has been used, and whether a detection result is attributed to reflection by a target or to aliasing is judged (refer to, for example, Japanese Patent No. 4238375).
However, when a plurality of transmitting antennas each having a different beam directivity are used, the directions of the transmitting antennas are required to be precisely decided, and a problem occurs in that manufacturing becomes difficult.
In addition, when application to an actual machine is considered, use of an electronic scanning method can also be considered in which, using an array antenna in which antenna elements are arrayed on a same plane instead of a plurality of antennas each having a different beam directivity, the direction of a transmission beam is changed by changing the phase of the transmission signal supplied to each antenna element configuring the array antenna and the like.
In this instance, as a phase controller that changes the phases of the transmission signals supplied to the array antenna, a phase shifter, a Rotman lens, a Butler matrix, and the like are known.
However, a problem occurs in that actualization of these phase controllers is difficult in terms of performance and cost.